>Date: Thu, 13 Jul 1995 08:20:27 -0400
>From: John Kohl <jtk@atria.com>
>
>While working on the GUS audio driver, I've been making assumptions
>about what PCM8 and PCM16 are supposed to mean for audio data formats.
>
>What is the difference between the two?  I don't think it's just sample
>size, because I recall seeing support in other drivers for both 8- and
>16-bit data in at least one of the formats.

[Sorry if you see this twice, my Emacs process died the first time and
I'm not sure my message got to the list.]

After taking another look at SunOS' audio(4) manpage and
<sun/audioio.h>, I think that the AUDIO_ENCODING_PCM{8,16} symbols
should Go Away.  When the encoding is AUDIO_ENCODING_LINEAR, the
driver should get the sample size from the 'precision' member of the
audio_prinfo structure.  Some redesign of the mixer interface will be
necessary.

>My working hypothesis has been:  PCM16/LINEAR is for 8- or 16-bit signed data;
>PCM8 is for 8-bit unsigned data.  There is no support for 16-bit
>unsigned data.  ULAW is for 8-bit Sun-style logarithmic encoding.  ALAW
>is for some format I haven't tackled yet.

Sun's audio(4) states that PCM data is always signed.  Either we
should define another symbol for unsigned data (e.g.
AUDIO_ENCODING_ULINEAR) or require that the hardware driver be
responsible for any necessary conversion (may be SLOW).

ULAW and ALAW are not defined by Sun; they are defined by CCITT (now
ITU) recommendation G.711.  ULAW is the standard digital format used
by the U.S. telephone system.  ALAW is a similar system used in
Europe.
-- 
Mike Long <mike.long@analog.com>           http://www.shore.net/~mikel
VLSI Design Engineer         finger mikel@shore.net for PGP public key
Analog Devices, CPD Division          CCBF225E7D3F7ECB2C8F7ABB15D9BE7B
Norwood, MA 02062 USA                assert(*this!=opinionof(Analog));